The present invention is described in the German priority applications No.10005550.8, filed Feb. 9, 2000, and No. 10040100.7, filed Aug. 16, 2000, which are hereby incorporated by reference as is fully disclosed herein.
The present invention relates to the field of azo colorants. Azo colorants are customarily produced in industry in batch operations in reaction vessels by mixing the starting materials together in aqueous phase (Fisher, Organische Chemie, Verlag Chemie, Weinheim/Bergstraxcex2e, 1965, p. 890 ff., 1431, 1796 ff.).
Another way is the continuous mixing of equivalent amounts of the starting materials in the form of aqueous acidic or aqueous alkaline solutions in, for example, mixing nozzles and continuous flow reactors with or without a postreaction phase in a reaction vessel (azo coupling: DE 1 544 453, EP 244 686; diazotization: EP-A-0 006 190).
The principal process operations involved are the diazotization of aromatic or hetaromatic amines and the azo coupling reaction. Certain azo pigments may subsequently require a metal exchange reaction (laking) and/or an aftertreatment in water/solvents to obtain the desired crystal properties. In the case of some azo dyes, a reaction is subsequently carried out to form metal complexes.
In all these processes, it is essential that the process parameters, such as temperature, time and (in the case of azo pigments) also in particular the degree of mixing, be controlled, if the products are to be pure and of high and consistent quality. One problem with these processes is the scaleup of new products from the laboratory scale to the large industrial scale.
It is an object of the present invention to provide a process for preparing azo colorants that provides optimal control of the process parameters, ensures improved mixing of the reactants and simplifies scaleup.
DD 246 257 A1 discloses the possibility of using miniaturized apparatuses for chemical reactions where the chemical entities to be treated are only available in small quantities or are very costly, so that large dead spaces in the equipment become unaffordable. DE 3 926 466 C2 describes strong exothermic chemical reactions of two chemical entities in a microreactor.
Microreactors for chemical reactions are constructed from stacks of grooved plates and are described in DE 39 26 466 C2 and U.S. Pat. No. 5,534,328. It is pointed out in U.S. Pat. No. 5,811,062 that microchannel reactors are preferably used for reactions that do not require or produce materials or solids that would clog the microchannels.
It has now been found that, surprisingly, microreactors are useful for carrying out diazotization and azo coupling and also metal exchange reactions or metal complexing reactions to prepare azo colorants, such as azo pigments and azo dyes.
As used herein, microreactor comprehends micro- and minireactors, which differ only by reason of the dimensions and construction of the reaction channel structures.
It is possible to use, for example, microreactors as known from the cited references or from publications of the Institut fxc3xcr Mikrotechnik Mainz GmbH, Germany, or else commercially available microreactors, for example Selecto(trademark) (based on Cytos(trademark)) from Cellular Process Chemistry GmbH, Frankfurt/Main.